The present invention relates to a sealed type appropriately-shaped information recording medium having a recording layer provided on the surface of at least one of the substrates for making optical recording and reproduction of information.
In manufacture of optical information recording media by sealing a pair of disc substrates with a spacer, adhesion techniques using an epoxy adhesive have been employed for bonding the substrates and spacer. Conventional epoxy adhesives can be reckoned as an excellent adhesive in that they exert no such baneful effects as reducing reflectance of the recording material of the disc and reducing the S/N ratio. However, such epoxy adhesives, because of their hot-curing property, may cause deformation of the substrates when heated and are also poor in productivity as a long time is required for curing and also jigs for fixing members during this operation are necessary.
For eliminating these problems, ultraviolet-curing resins containing a radical photopolymerization initiator have been developed and are now practically used as a new sealing adhesive. These ultraviolet-curing resins, although free of said defects of epoxy adhesives, have given rise to the new problem that the squeezed-out portion of the sealing adhesive, when contacted with air, remains uncured due to their anaerobic nature, this resulting in causing a reduction of reflentance of the recording material of the disc or a reduction of S/N ratio.
In addition, another new epoxy sealing adhesives comprising a cation polymerization photoinitiator which is selected from onium salts, the counterions being, for example, SbF.sub.6.sup.-, PF.sub.6.sup.-, As.sub.2 F.sub.5.sup.-, and BF.sub.4.sup.-, were used. But, these photoinitiators of the onium salt type, although free of said defects of ultraviolet-curing resins containing a radical photopolymerization initiator, gave also rise to the new problem that the optical recording medium containing organic dyes are attacked with the strong acid produced on curing possibly from the counter ion.
As a solution to said problem, the present inventors had previously proposed use of an adhesive composed of (a) an epoxy resin, (b) a photolyzable organosilicon compound and (c) a metal complex type composite catalyst. After this proposal, the present inventors have pursued their further studies on the photolyzable organosilicon compounds in this type of adhesives, and as a result, found that a photolyzable organosilicon compound having both of o-nitrobenzyloxy group and fluorine-containing phenyl group is especially excellent as a component of sealing adhesive for the optical information recording media.
An object of the present invention is to provide an improved sealing technique for the sealed type optical information recording media.